Adenylate/uridylate-rich element (ARE)-mediated mRNA turnover is an important regulatory component of gene expression for innate and specific immunity, in the hematopoietic system, in cellular growth regulation, and for many other cellular processes. This diversity is reflected in the distribution of AREs in the human genome, which we have established as a database of more than 900 ARE-containing genes that may utilize AREs as a means of controlling cellular mRNA levels. The p38 mitogen-activated protein kinase (MAP kinase) pathway has been implicated in regulating the stability of nine ARE-containing transcripts. Here we explored the entire spectrum of ARE-containing genes for p38-dependent regulation of ARE-mediated mRNA turnover with a custom cDNA array containing probes for 950 ARE mRNAs. The human monocytic cell line THP-1 treated with lipopolysaccharide (LPS) was used as a reproducible cellular model system that allowed us to precisely control the conditions of mRNA induction and decay in the absence and presence of the p38 inhibitor SB203580. This approach allowed us to establish an LPS-induced ARE mRNA expression profile in human monocytes and determine the half-lives of 470 AU-rich mRNAs. Most importantly, we identified 42 AU-rich genes, previously unrecognized, that show p38-dependent mRNA stabilization. In addition to a number of cytokines, several interesting novel AU-rich transcripts likely to play a role in macrophage activation by LPS exhibited p38-dependent transcript stabilization, including macrophage-specific colony-stimulating factor 1, carbonic anhydrase 2, Bcl2, Bcl2-like 2, and nuclear factor erythroid 2-like 2. Finally, the identification of the p38-dependent upstream activator MAP kinase kinase 6 as a member of this group identifies a positive feedback loop regulating macrophage signaling via p38 MAP kinase-dependent transcript stabilization.The regulation of mRNA stability is an important factor in modulating gene expression, in particular for transiently expressed genes that require tightly controlled mRNA levels. For different cytokines, growth factors, and proto-oncogenes with short mRNA half-lives, modulating the decay rate involves adenylate/uridylate (AU)-rich elements (AREs), often consisting of one to several copies of the sequence AUUUA located in the 3Ј untranslated region (12). With a bioinformatics approach, we previously identified several hundred ARE-containing genes that were compiled in the ARE mRNA database (ARED) (2). These genes encode a wide variety of proteins, implicating ARE-mediated mRNA decay in a broader spectrum of cellular processes than was previously recognized.The molecular mechanisms by which AREs are used to fine-tune mRNA turnover are thought to involve specific RNA-binding proteins (33,34). trans-Acting factors from different protein families that bind AREs and influence mRNA degradation have been identified. The Hu family proteins HuR and HuB have been shown to bind many different AU-rich messages and stabilize these in several different cell systems ...

Hepatitis C virus (HCV), a major cause of liver disease worldwide, is frequently resistant to the antiviral alpha interferon (IFN). The HCV nonstructural 5A (NS5A) protein has been implicated in HCV antiviral resistance in many studies. NS5A antagonizes the IFN antiviral response in vitro, and one mechanism is via inhibition of a key IFN-induced enzyme, the double-stranded-RNA-activated protein kinase (PKR). In the present study we determined if NS5A uses other strategies to subvert the IFN system. Expression of full-length NS5A proteins from patients who exhibited a complete response (FL-NS5A-CR) or were nonresponsive (FL-NS5A-NR) to IFN therapy in HeLa cells had no effect Alpha interferon (IFN) is a Food and Drug Administrationapproved treatment for chronic HCV infection. Only 8 to 12% of patients with HCV genotype 1 have a sustained clinical virological response to IFN therapy (4,43,61). Recently, combination therapy with interferon and the guanosine analogue ribavirin was shown to be superior to IFN monotherapy in producing sustained biochemical and virological responses (9,45,62). However, despite the significant improvement in rates of sustained response, as many as 60% of patients with hightiter HCV genotype 1 infection are nonresponsive to combination therapy.When IFN binds to its receptor, two receptor-associated tyrosine kinases of the STAT/JAK family, Tyk2 and Jak1, become activated. These activated kinases phosphorylate STAT-1 and STAT-2 on a single conserved tyrosine residue (8). STAT-1 and STAT-2 form heterodimers and combine with the p48 protein to form an active transcription factor known as IFN-stimulated gene factor 3 (ISGF-3). ISGF-3 binds to a common element termed the interferon-stimulated response element (ISRE), found in the promoter regions of all IFNstimulated genes, whereupon transcription occurs. Expression of the entire HCV polyprotein has been shown to inhibit IFNinduced STAT/JAK signaling in human U2-OS osteosarcoma cells (25). It was not reported which HCV protein was responsible for this effect.Recent studies have led to exciting discoveries in the emerging research area of the roles of HCV proteins in antiviral resistance. Two examples are the interaction of the HCV non-* Corresponding author. Mailing address:

β-catenin plays an essential role in several biological events including cell fate determination, cell proliferation, and transformation. Here we report that β-catenin is encoded by a labile transcript whose half-life is prolonged by Wnt and phosphatidylinositol 3-kinase–AKT signaling. AKT phosphorylates the mRNA decay-promoting factor KSRP at a unique serine residue, induces its association with the multifunctional protein 14-3-3, and prevents KSRP interaction with the exoribonucleolytic complex exosome. This impairs KSRP's ability to promote rapid mRNA decay. Our results uncover an unanticipated level of control of β-catenin expression pointing to KSRP as a required factor to ensure rapid degradation of β-catenin in unstimulated cells. We propose KSRP phosphorylation as a link between phosphatidylinositol 3-kinase–AKT signaling and β-catenin accumulation.

Hepatitis C virus (HCV), a major cause of liver disease worldwide, is frequently resistant to the antiviral alpha interferon (IFN). We have recently found that the HCV NS5A protein induces expression of the proinflammatory chemokine IL-8 to partially inhibit the antiviral actions of IFN in vitro. To extend these observations, in the present study we examined the relationship between levels of IL-8 in serum, HCV infection, and biochemical response to IFN therapy. Levels of IL-8 were significantly elevated in 132 HCV-infected patients compared to levels in 32 normal healthy subjects and were also significantly higher in patients who did not respond to IFN therapy than in patients who did respond to therapy. This study suggests that HCV-induced changes in levels of chemokine and cytokine expression may be involved in HCV antiviral resistance, persistence, and pathogenesis.Chronic hepatitis C virus (HCV) infection is a significant clinical problem throughout the world. About 85% of people infected with HCV develop chronic infection, and approximately 70% of patients develop histological evidence of chronic liver disease (9).Interferon (IFN) and the guanosine analogue ribavirin are widely used treatments for chronic HCV infection (5,11,17). However, as many as 60% of patients with high-titer HCV genotype 1 infections remain nonresponsive to combination therapy.The HCV NS5A protein has been implicated in the resistance of HCV to antiviral therapy (reviewed in reference 14). We have recently found that NS5A induces the CXC chemokine interleukin 8 (IL-8) to inhibit the antiviral actions of IFN in vitro (15). To investigate the clinical significance of these results, in this study we investigated the relationship among levels of IL-8 and tumor necrosis factor alpha (TNF-␣) (a potent inducer of ) in serum, HCV infection, and response to IFN therapy.One hundred thirty-two patients from Saudi Arabia with hepatitis C disease were studied. Diagnosis was reached using appropriate serological, virological, biochemical, and histological criteria. All sera from patients diagnosed to have chronic hepatitis C showed elevated liver enzymes, tested positive for anti-HCV antibodies by a second-generation enzyme-linked immunosorbent assay (ELISA), and were confirmed to be reactive with HCV recombinant immunoblot assay-2. Patients with hepatitis B surface antigen positivity, autoimmune disease, alcohol-or drug-induced liver diseases, hepatic failure, decompensated cirrhosis, schistosoma mansoni, or hematological abnormalities were excluded from the study. Genotypes were not determined, although the predominant HCV genotypes in Saudi Arabia are genotype 4 and 1 (2, 19). IFN-␣2a was administered intramuscularly three times per week at 3 million U per dose. The study was performed with the approval of the King Faisal Specialist Hospital and Research Centre research advisory council. Response to therapy was assessed biochemically based on normalization of alanine aminotransferase values 6 months after termination of therapy.To measure IL-8 ...